Alpha-amylases (alpha-1,4-glucan-4-glucanohydrolases, E.C. 3.2.1.1) constitute a group of enzymes, which catalyses hydrolysis of starch and other linear and branched 1,4-gluosidic oligo- and polysaccharides.
There is a long history of industrial application of alpha-amylases in e.g. detergent, baking, brewing, starch liquefaction and saccharification such as in preparation of high fructose syrups or as part of ethanol production from starch. Many of these and other applications of alpha-amylases utilize alpha-amylases derived from microorganisms, in particular bacterial alpha-amylases.
Among the first bacterial alpha-amylases to be used were an alpha-amylase from B. licheniformis, also known as Termamyl, which has been extensively characterized and the crystal structure has been determined for this enzyme. Alkaline amylases, such as the alpha-amylase derived from Bacillus sp. as disclosed in WO 95/26397, form a particular group of alpha-amylases that have found use in detergents. Many of these known bacterial amylases have been modified in order to improve their functionality in a particular application.
Termamyl and many highly efficient alpha-amylases required calcium for activity. The crystal structure for Termamyl was found that four calcium atoms were bound in the alpha-amylase structure coordinated by negatively charged amino acid residues. In other alpha-amylases the amount of calcium ions bound in the structure might be different. This requirement for calcium is a disadvantage in applications where strong chelating compounds are present, such as in detergents or during ethanol production from whole grains.
As mentioned above it is well known that a number of enzymes are dependent on calcium or other metal ions such as magnesium or zinc for both activity and stability, hence it is a challenge to develop enzymes which are both stable and show good performance in compositions comprising a chelating agent, e.g. detergents containing chelating agents or compositions for use in the production of biofuel wherein the plant material or the starch-containing material has a natural content of chelating agents such as e.g. phytic acid. Chelating agents are e.g. added or incorporated to reduce the water hardness during wash, protect bleaching agents that may also be present, and chelating agents also have a direct effect on the removal of some stains. The stability of a calcium dependent enzyme in a detergent can sometimes be improved by addition of calcium to the detergent, but often this will then destroy the stain removing effect. Furthermore, addition of calcium to a liquid detergent may present problems with the formulation, i.e. the physical stability of the detergent.